Abstract 4310: Predictive biomarkers of tumor sensitivity to STEAP1 antibody-drug conjugate (ADC) in patients (pts) with metastatic castration-resistant prostate cancer (mCRPC)

83 Background: The abundant expression of prostate-specific membrane antigen (PSMA) on prostate cancer cells provides a rationale for antibody therapy. PSMA antibody drug conjugate (ADC) is a fully human antibody to PSMA linked to the microtubule disrupting agent monomethyl auristatin E (MMAE). It binds PSMA and is internalized and cleaved by lysosomal enzymes releasing free MMAE causing cell cycle arrest and apoptosis. We enrolled 70 patients (pts) in a phase II trial of PSMA ADC in taxane-refractory metastatic castration-resistant prostate cancer (mCRPC). Methods: Pts with progressive mCRPC following taxane and ECOG PS 0 or 1 were eligible. PSMA ADC was administered Q3 week IV for up to eight cycles. Safety, tumor response by prostate-specific antigen (PSA), circulating tumor cells (CTC), imaging, biomarkers and clinical progression were assessed. Dosing was initiated at 2.5 mg/kg and adjustment for tolerability was allowed. Results: Thirty five pts began treatment at 2.5 mg/kg. Due to neutropenia, the remaining 35 pts began at 2.3 mg/kg. All pts received prior docetaxel and abiraterone and/or enzalutamide. Forty one percent also received cabazitaxel. Adverse events (AEs) were consistent with what was seen in phase I; most common significant AEs were neutropenia (grade 4, 6.7% and 11.4% at 2.3 and 2.5 mg/kg, respectively) and peripheral neuropathy (grade 3 or higher, 6.7% (2.3) and 5.7% (2.5)). Two pts at 2.5 mg/kg died of sepsis. 43% of pts at 2.3 and 37% of pts at 2.5 had declines in CTC from 5 or more to less than 5 cells/7.5 ml blood and 57.1% (2.3) and 74.1% (2.5) had 50% or more CTC declines; 26.1% (2.3) and 16.1% (2.5) had PSA declines of 30% or more thus far. PSA and CTC responses were associated with higher PSMA expression on CTC and lower neuroendocrine (NE) markers. The CTC conversion rate (5 or more to less than 5) was approximately 80% in pts with low NE markers. Prior cabazitaxel or abiraterone and/or enzalutamide did not appear to affect response. Centralized assessments of images by RECIST of all pts are currently planned and will be presented. Conclusions: PSMA ADC at 2.3 mg/kg was generally well tolerated in pts with progressive mCRPC previously treated with taxane. Anti-tumor activity, CTC and PSA reductions were observed at 2.3 and 2.5 mg/kg. Updated safety, tumor response and radiographic assessments from the full cohorts of 2.3 and 2.5 mg/kg will be presented. Testing in taxane naïve pts is also ongoing. Clinical trial information: NCT01695044.

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Rovalpituzumab tesirine (Rova-T) as a therapeutic agent for Neuroendocrine Prostate Cancer (NEPC).

Journal of Clinical Oncology ◽

10.1200/jco.2017.35.15_suppl.5029 ◽

2017 ◽

Vol 35 (15_suppl) ◽

pp. 5029-5029 ◽

Cited By ~ 3

Author(s):

Loredana Puca ◽

Verena Sailer ◽

Kaitlyn Gayvert ◽

Kumiko Isse ◽

Michael Sigouros ◽

...

Keyword(s):

Prostate Cancer ◽

Cell Surface ◽

Cell Lines ◽

Therapeutic Agent ◽

Cellular Proliferation ◽

Prostate Adenocarcinoma ◽

Antibody Drug Conjugate ◽

Drug Conjugate ◽

Castration Resistant ◽

Antibody Drug

5029 Background: TheNotch ligand Delta like ligand 3 (DLL3) is aberrantly expressed on the cell surface of small cell lung cancer (SCLC), and the DLL3-antibody drug conjugate, Rova-T, has shown promise for patients with SCLC (Rudin et al, Lancet Onc 2017). NEPC is a late stage subtype of castration resistant prostate cancer with limited therapeutic options. Based on clinical and molecular similarities with SCLC, we investigated expression of DLL3 and the use of Rova-T in NEPC. Methods: We evaluated mRNA and/or protein expression of DLL3 in a cohort of 395 patients (535 samples) ranging from benign prostate (BEN), localized prostate adenocarcinoma (PCA), castration resistant adenocarcinoma (CRPC), and NEPC and correlated with pathologic and genomic features. Prostate cancer cell lines and patient-derived organoids were treated with Rova-T (SC16LD6.5) in vitro and in vivo. Results: DLL3 was expressed at the mRNA and/or protein level in 0/143 BEN (0%), 4/266 PCA (1%), 8/76 CRPC (10%), 33/50 NEPC (66%). DLL3 IHC was of higher intensity in NEPC and co-localized with classical NE marker expression (SYP, CGA). DLL3 was amongst the most differentially expressed genes by RNA-seq in NEPC versus CRPC (p = < 0.0001, fold change = 71), correlated with ASCL1 expression (r = 0.88) and RB1 genomic loss (83%), and inversely with AR expression. Although treatment with the Notch inhibitor DAPT suppressed Notch target gene expression in NEPC, DAPT did not have significant effect on cellular proliferation. siRNA knockdown of DLL3 or DAPT did not alter AR signaling or NE markers. Rova-T (SC16LD6.5) was active in DLL3-positive NEPC cell lines with an IC50 of 580pM compared to the control IgG1LD6.5 (IC50 = 6.3nM), whereas CRPC lines were insensitive. Conclusions: DLL3 is a cell surface protein aberrantly expressed in the majority of NEPC and a subset of CRPC, and is not expressed in primary prostate cancer or benign tissues. The DLL3 antibody-drug conjugate Rova-T demonstrates preferential preclinical activity in NEPC compared to prostate adenocarcinoma. These data support further investigation of Rova-T as a potential therapeutic agent for NEPC. A phase I trial with dedicated NEPC arm is currently accruing patients (NCT02709889).

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870 A phase 2 trial of prostate specific membrane antigen antibody drug conjugate (PSMA ADC) in taxane-treated metastatic castration-resistant prostate cancer (MCRPC)

European Urology Supplements ◽

10.1016/s1569-9056(14)60857-5 ◽

2014 ◽

Vol 13 (1) ◽

pp. e870 ◽

Cited By ~ 3

Author(s):

D. Petrylak ◽

D.C. Smith ◽

L.J. Appleman ◽

M. Fleming ◽

A. Hussain ◽

...

Keyword(s):

Prostate Cancer ◽

Prostate Specific Membrane Antigen ◽

Phase 2 ◽

Castration Resistant Prostate Cancer ◽

Antibody Drug Conjugate ◽

Phase 2 Trial ◽

Castration Resistant ◽

Antigen Antibody ◽

Specific Membrane ◽

Antibody Drug

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Phase I Study of DSTP3086S, an Antibody-Drug Conjugate Targeting Six-Transmembrane Epithelial Antigen of Prostate 1, in Metastatic Castration-Resistant Prostate Cancer

Journal of Clinical Oncology ◽

10.1200/jco.19.00646 ◽

2019 ◽

Vol 37 (36) ◽

pp. 3518-3527 ◽

Cited By ~ 4

Author(s):

Daniel C. Danila ◽

Russell Z. Szmulewitz ◽

Ulka Vaishampayan ◽

Celestia S. Higano ◽

Ari D. Baron ◽

...

Keyword(s):

Prostate Cancer ◽

Tumor Cells ◽

Dose Escalation ◽

Specific Antigen ◽

Castration Resistant Prostate Cancer ◽

Antibody Drug Conjugate ◽

Castration Resistant ◽

Grade 3 ◽

Recommended Phase Ii Dose ◽

Antibody Drug

PURPOSE Six-transmembrane epithelial antigen of the prostate 1 (STEAP1) is highly expressed in prostate cancers. DSTP3086S is a humanized immunoglobulin G1 anti-STEAP1 monoclonal antibody linked to the potent antimitotic agent monomethyl auristatin E. This study evaluated the safety and activity of DSTP3086S in patients with metastatic castration-resistant prostate cancer. METHODS Patients were enrolled in a 3 + 3 dose escalation study to evaluate DSTP3086S (0.3 to 2.8 mg/kg intravenously) given once every 3 weeks followed by cohort expansion at the recommended phase II dose or weekly (0.8 to 1.0 mg/kg). RESULTS Seventy-seven patients were given DSTP3086S once every 3 weeks, and seven were treated weekly. Two patients in the once-every-3-weeks dose escalation had dose-limiting grade 3 transaminitis. Grade 3 hyperglycemia and grade 4 hypophosphatemia were dose-limiting toxicities in one patient treated at 1.0 mg/kg weekly. Initial cohort expansion evaluated dosing at 2.8 mg/kg once every 3 weeks (n = 10), but frequent dose reductions led to testing of 2.4 mg/kg (n = 39) in the expansion phase. Common related adverse events (> 20%) across doses (once every 3 weeks) were fatigue, peripheral neuropathy, nausea, constipation, anorexia, diarrhea, and vomiting. DSTP3086S pharmacokinetics were linear. Among 62 patients who received > 2 mg/kg DSTP3086S once every 3 weeks, 11 (18%) demonstrated a ≥ 50% decline in prostate-specific antigen; two (6%) of 36 with measurable disease at baseline achieved a radiographic partial response; and of 27 patients with informative unfavorable baseline circulating tumor cells ≥ 5/7.5 mL of blood, 16 (59%) showed conversions to favorable circulating tumor cells < 5. No prostate-specific antigen or RECIST responses were seen with weekly dosing. CONCLUSION DSTP3086S has acceptable safety at the recommended phase II dose level of 2.4 mg/kg once every 3 weeks. Antitumor activity at doses between 2.25 and 2.8 mg/kg once every 3 weeks supports the potential benefit of treating STEAP1-expressing metastatic castration-resistant prostate cancer with an STEAP1-targeting antibody-drug conjugate.

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